1. Field of the Invention
The present invention generally relates to a video signal processing system and related method for calibrating an analog to digital converter of the video signal processing system. More specifically, the present invention relates to a video signal processing system and related method for calibrating analog to digital converter when video signals have no content during a horizontal blanking period.
2. Description of the Prior Art
Analog to digital converters (ADC) are utilized broadly in signal processing systems for converting analog signals into digital signals. Calibrations of ADCs are usually accomplished before hardwares of the ADCs leave the factory. However, the performance of ADC is distorted as long as the ADC is used.
Please refer to FIG. 1. FIG. 1 is a diagram of response of a prior art ADC. In FIG. 1, the transverse axis represents voltage levels of input analog signals, and the vertical axis represents magnitudes of output digits. Line S1 is the ideal response of the prior art ADC, and line S2 is the real response of the prior art ADC after being used for a period of time. First of all, the slopes of line S1 and line S2 are different. Second, the offset of the response of the prior art ADC drifts an amount of D1. These distortions decrease the accuracy of ADCs seriously. Besides, the shifts of dc-level of input signals can also ruin the performance of the ADC.
In video signal processing systems, such as TVs, digital TVs, etc., performance and accuracy of ADCs are very important for the quality of displaying images. Due to the lack of ability to calibrate the ADCs dynamically after the ADCs leave the factory, video signal processing systems can do nothing about the degradation of performance of ADCs.